The most important of the pasta filata cheeses is mozzarella, which may be made from buffaloes' milk, cows' milk or a mixture of the two and which can be produced in several varieties as described in more detail below. Because of the importance of the mozzarella cheeses, the invention is hereafter principally described with reference to its use in the production of mozzarella, but it may also be applied mutatis mutandis to the production of other pasta filata cheeses, including Scarmorza, Scamorzina, Provola, Burrino, Manteca, Provolone which may be produced in several shapes having different names (e.g. Topolino, Pancetta, Pancettone, Mandarino), Caciocavallo, Ragusano and Silano, differing from one another in the duration of ripening and consistency.
Conventional mozzarella and other pasta filata type cheeses are characterised by a unique plasticising and kneading treatment, which is carried out on the fresh curd in hot water. This treatment imparts to the finished cheese its characteristic stretching and melting properties, as well as its fibrous structure.
The primary use of mozzarella is in cooking, and it is the preferred cheese for pizza. Pasta filata cheeses are also used, for example, as a snack food in the form of short sticks popularly known as "string cheese". Mozzarella is also often consumed fresh as a table cheese. High moisture mozzarella is typically used fresh and low moisture mozzarella is more suitable for shredding and use in food service.
There are several methods for the manufacture of pasta filata type cheeses, but all have certain features in common. Typically, a starter culture is added to pasteurised milk. Sufficient rennet is subsequently added, to set the curd. The resulting coagulum is cut, scalded (cooked) at about 30.degree. C. to 40.degree. C., cheddared, and then subjected to the plasticising process at a temperature in the range of 55.degree. C. to 75.degree. C. The hot plastic curd is then moulded into the desired shape, and salted and cooled in chilled brine for approximately 2 to 24 hours. After the brining step, mozzarella cheese is traditionally aged for 7 to 21 days to develop the characteristic texture and functionality. High moisture mozzarella may be made using a mesophillic starter and cooking to 32.degree. C. to 35.degree. C. Mozzarella intended for use as a pizza ingredient is not necessarily aged for as long as 7-21 days but, instead, is conventionally aged at most overnight, after which it is shredded, and then frozen, to be kept until it is needed.
A widely practised alternative to using a starter culture in the manufacture of both high and low moisture mozzarella is direct acidification. This typically involves the addition of an organic or inorganic acid, usually acetic acid, although lactic, citric and hydrochloric acids are all used in the trade. Acid precursors, such as gluconodelta lactone (GDL), which slowly breaks down to produce lactic acid, may also be used.
Numerous attempts have been made to improve the stage of manufacture where working and stretching of the raw curd is required. These attempts have been largely of a mechanical nature.
U.S. Pat. No. 3,692,540 describes a method where the curd is held in the whey until the acidity reaches 0.25-0.30%, and the raw curd pieces are then heated without working at a temperature of 54.degree. C.-71.degree. C.
U.S. Pat. No. 5,431,931 discloses a method for making low fat mozzarella where cultured skimmed milk is added to the cheese milk so that the amount of rennet can be reduced by one half. The cheese is then worked and stretched at 60.degree. C.
EP-A-535 268 discloses a method to reduce the ageing time of mozzarella cheese by controlling the composition of the cheese and preferably mixing salt with the raw curd prior to the heating-stretching step.
The ageing period can also be shortened by the addition of sodium citrate (CZ-A-141,283) and by injecting a pregastric esterase solution (Lee et al, 1978, Process Biochemistry).
International patent application WO91/13553 discloses a method wherein Bacillus licheniformis protease is used to improve the meltability of Mozzarella made using ultra-filtered milk. The protease degrades whey proteins without interfering with the renneting process.
Stretching in mozzarella cheese is thought to require free calcium in association with the unravelling of the complex protein structure induced by heating. Meltability is both related directly to moisture and fat contents as well as salt concentration (Kindstedt, 1993, Critical Reviews in Food Science and Nutrition).
Oberg et al (J Dairy Science 1992) investigated the effect of different forms of rennet on the functionality of Mozzarella cheese and showed that stretch was significantly affected by the rennet used and storage time. Porcine pepsin produced cheese with the greatest stretch.
Oberg et al (J Dairy Science 1991) investigated the effect of proteolytic activity in starters typically used for Mozzarella manufacture. They found that protease positive starters produced Mozzarella with increased browning and stretch compared with direct acidified cheese, but with no difference in stretch between protease positive and protease negative starters. All cultured cheese had greater stretch than direct acidified cheese.
Thus, the literature identifies that proteolysis has an effect on functional properties but makes no clear conclusions from sometimes conflicting observations.